A heater for a grain bin, grain dryer, or the like in which air is heated by a gas fired burner and then inducted into a grain bin, grain dryer, or other structure for drying or otherwise conditioning grain therein. Conventionally as shown in FIGS. 1-5, such heaters include an outer housing 130 which may be connected to a grain bin 10 for directing heated air therefrom into the grain bin 10. A fan 34 forcefully moves air through the outer housing 130, past a burner 144 therein, and directs the heated air into the grain bin 10. Oftentimes, the grain bin 10 has a perforated floor 18 raised above a concrete pad 12 with the space between the floor 18 and the concrete pad 12 constituting a plenum 22. The heater 24 directs heated air under pressure into this plenum 22 where it is substantially uniformly distributed under the entire cross section of the grain bin 10 such that the heated air may pass upwardly through the floor 18 and through the grain supported on the floor 18 so as to dry the grain.
Typically, most grain bin dryers are gas fired dryers which burn either liquefied petroleum (e.g., liquid propane) or natural gas, such as the grain bin dryer of U.S. Pat. No. 5,400,525 which is incorporated by reference herein. The dryer fan may be either an axially blower located upstream from the heater and generally in axial alignment with the heater, or the fan may be a centrifugal fan (not illustrated) coupled to the heater upstream from the heater. Such heaters 24 typically include a gas burner 144 positioned within the central portion of the heater outer housing 130 so that when the gas fuel is ignited, a flame is generated which heats the air forced by the fan through the heater outer housing 130 and into the grain bin 10. It has been long known that by providing such gas fired grain bin heaters 10 with a flame diverter 170 that the flame can be more uniformly distributed within the outer housing 130 thus resulting in better heating of the air being forced through the heater 24. Typically, such prior art flame diverters comprise a plurality of spaced slats 182 arranged in a generally conical configuration with the apex of the conical flame diverter 170 being positioned close to the burner 144 at the center of the heater outer housing 130 so as to direct the flame outwardly toward the walls of the outer housing 130. Typically, these flame diverter slats 182 are provided with a multiplicity of holes 183 therein so as to aid in supplying air to the air/fuel mixture.
In a gas burner, the gas fuel has a certain calorific value typically expressed in BTU/cubic foot of the gas fuel. For example, natural gas may have a calorific value of about 1,000 BTU/cu. ft., and commercially available propane (L.P.) gas may have a calorific value of about 2,350 BTU/cu. ft. If these gaseous fuels are completely combusted, the products of combustion will include carbon dioxide, water, and nitrogen compounds from the combustion air. Of course, complete combustion insures the maximum release of heat from the fuel and results in the most efficient operation of the burner. Complete combustion of the fuel results in the maximum amount of air being heated. Usually, complete combustion of the fuel is visually evidenced by the flame burning with a bluish or colorless flame. If combustion is incomplete, as will be the case if there is not sufficient air for complete combustion, carbon monoxide and carbon will also make up part of the combustion products. It is well recognized that the presence of a “yellowish” flame is a sign that incomplete combustion (and thus less efficient combustion) is occurring such that the maximum efficiency of the burner is not being realized.
In many prior art grain dryer heaters such as above-described, it has long been noted that at least certain portions of the flame within the burner had a generally yellowish appearance which is an indication of incomplete combustion. Typically, such areas of incomplete combustion were immediately downstream from the burner nozzle located at the center of the grain bin heater housing. However, with the known prior art burners it has not heretofore been possible to regulate the position of the flame within the heater housing so as to achieve both complete combustion and to divert the flame outwardly toward the walls of the housing so as to result in a more evenly distributed heating of the air. The above-described flame diverters with their spaced slats did effectively direct the flames outwardly from the burner toward the walls of the housing, but such flame diverters (even when their spaced slats were provided with a multiplicity of holes therein) were not effective so as to insure that substantially complete combustion of the gaseous fuel would result even if the burner was regulated to admit more air into the burner for mixing with the fuel prior to the point the fuel was ignited. As above-noted, in conventional prior art grain bin dryers, a region of low pressure would develop immediately downstream from the burner nozzle such that when the fuel burned in this area, it would burn with a “yellowish” color flame generally indicative of incomplete combustion.
To address the low pressure region, U.S. Pat. No. 5,400,525 disclosed a burner which includes a conical-shaped flame cone within the low pressure region of the flame diverter downstream from burner nozzle on the inside of the flame diverter. By placing the flame cone on the downstream side of the flame diverter in the region of normally low pressure, the combusting air/fuel mixture is diverted from this low pressure region and is at least partially confined between the inner faces of flame diverter and the outer face of the flame cone such that excess air forced through openings in diverter slats and excess air flowing around the slats is mixed with the combusting air/fuel mixture thereby to result in more complete combustion of the air/fuel mixture. As a result of the flame cone, substantially the entire quantity of the air/fuel mixture burns with a generally colorless or “blue” flame which is visually indicative of more complete combustion of the fuel. Of course, such combustion results in the maximum amount of heat being released from the fuel such that the efficiency of the burner is increased as indicated in the chart of FIG. 15 herein. In addition, as the air flowing through the housing encounters the flame diverter and flame cone, the air and the flames are intermixed and are forced to spread radially outwardly toward the housing walls. While this design increases the efficiency of the burner, the burner disclosed below provides even further increased efficiency.
Thus, there has been a long-standing problem as to how to maximize combustion to maximize efficiency of the heater and to simultaneously uniformly distribute the heated air with the air forcefully moved through the heater without duly restricting the flow of air through the blower/heater unit.